The invention relates to a method of joining together the marcinal portions of a printing plate for a rotary press. The invention also relates to the printing plate produced in accordance with the method. In order to increase the output of rotary presses, it has already been proposed to replace the copper coating on the printing roller by a matrix which forms the printing plate and the outer coating of which consists of a photosensitive material.
Since such matrices are usually produced as flat blanks it is necessary to join the two marginal portions of the blank together and mount this printing plate accurately and in a fixed position on the printing roller. It has already been proposed to connect the two ends of the printing plate by step punching step, in order thus to establish a positive mutual joint of the plate ends. These punchings which provide connection between the marginal portions of a positive of the plate prevent a separation of the marginal portions in the tangential direction of the cylinder. In the known design, an adhesive or a hardenable material is provided on the plate surface in order to prevent separation of the marginal portions of the plate which have been joined together. This filling material is also provided in order to ensure the continuity and smoothness, required for printing plates, of the surface at the butt joint. Such a printing plate is used in a cylinder which is extensible in the radial direction and has magnetic holding devices which fix the ends of the printing plate on the periphery of the printing roller.
This known type of plate joining has various disadvantages. On the one hand, a special and, above all, highly accurate working of the two marginal portions is necessary (punching step) in order to allow positive joining of the marginal portions. Furthermore, the punchings for positive joining necessarily have considerable dimensions, which substantially restrict the useful area for applying the print image to the plate. Moreover, the printing plate described can be used only together with a cylinder of particular design. The known plates are not interchangeable and, in most cases, the positive joint must be made directly on the printing roller on which the printing plate is used.